In the present invention, CD8+ conventional dendritic cells (CD8+ cDCs) and equivalents thereof (eCD8+ cDCs) in mouse and human have been established as major source of IFN-lambda (IFN-&lambda；) in response to double-stranded (ds) nucleic acids. The invention relates to therapeutic applications of ds nucleic acids or analogs thereof targeting CD8+ and/or eCD8+ cDCs in the prevention and/or treatment of infectious diseases, preferably viral infections, or cancer. Furthermore, the invention relates to an in vitro method for producing IFN-&lambda； and/or generating or obtaining a population of IFN-&lambda； producing CD8+ or eCD8+ cDCs as well as in vitro method for detecting or screening for CD8+ and/or eCD8+ cDCs. In addition, the invention relates to a Flt3-ligand or a M-CSF receptor ligand for use in increasing the level of CD8+ and/or eCD8+ cDCs in a subject suffering from an infectious disease or cancer.
